In general, in a hoisting machine, a gear mechanism configured to be capable of lifting a heavy load with a small force is provided between a hand wheel rotated by an operation of a hand chain and a load sheave to move up and down a load chain to which a load is applied. Because the gear mechanism in the hoisting machine is a decelerating mechanism to decelerate a rotation of the hand wheel and transmit the decelerated rotation to the load sheave, the rotation of the load sheave is always decelerated regardless of existence and non-existence of a load. This results in the lowering of work efficiency.
Therefore, it is proposed to provide a variable speed mechanism to be variable the rotation speed of the load sheave depending on existence and non-existence or high or low of a load. For example, there is proposed an automatic transmission which includes a first clutch means to transmit as is a rotation from a hand wheel, a second clutch means to transmit to a speed increasing mechanism, and a transmitting plate to engage and disengage the first clutch means and the second clutch means, and when a load is applied to the load sheave, wherein the first the transmitting plate is moved to engage the first clutch means and disengage the second clutch means, the winding up speed of the load chain is switched from a high speed to a low speed, if no load is applied, the second clutch means is engaged so that the winding up speed is at a high speed (see Patent Document 1).
In the automatic transmission, because the transmitting plate is axially moved to press the first clutch means and the second clutch means and press-fit them, and thereby a speed is switched, there is a problem that a switching resistance is large and operational sensing is poor. In addition, because the transmitting plate and so on are disposed axially and moved axially, there are problems that the transmission becomes axially large in size, only one side of the hoisting machine is heavy so that the hoisting machine becomes unbalance, and the hoisting machine is difficult to be operated due to inclination of the hoisting machine, because the transmission is disposed between the hand wheel and a break.
Moreover, in addition to this, there is proposed a load sensing-type transmission which includes a low speed rotation member, a high speed rotation member, and an output rotation member, wherein a magnetic body is provided on each of the foregoing members, and the members are mechanically engaged, after the magnetic bodies are magnetically engaged (see Patent Document 2).
However, in this transmission, an unstable engagement state due to a magnetic force is generated when a speed is switched, and therefore there is risk of idling. In addition, in the transmission, parts having complicate shapes formed by the magnetic bodies are frequently used; there is a problem that the transmission has a complicate structure, a large weight, and a high cost. In addition, even in the transmission, because the parts are axially disposed and moved axially, there are problems that the transmission is large in size and a balance of the transmission is poor when the transmission is applied to the hoisting machine. In particular, because the transmission is disposed between the hand wheel and the break, balance is very poor.